1. Field of the Invention:
The present invention relates to sighting devices, and more particularly to laser beam sighting assemblies useful in aligning pipe segments and flanges in the course constructing a pipeline.
2. Description of the Prior Art
The process of constructing a pipeline or pipe run often entails a sequence of welds in which long segments of pipe are joined to bend segments and flanges. In this process the accumulated build up of welding tolerances and welding heat distortions require continuous realignment sighting, with compensating grinding adjustments made at each weld joint. Thus the pipe fitter is constantly measuring angles, adjusting the weld lines and re-sighting in order to obtain a proper drainage slope and a true flange surface at the end of a run.
Maintaining a proper slope and flange surface alignment is particularly difficult at a pipeline bend. Here the length tolerances compound the angular tolerances and the pipe fitter therefore needs to adjust both the length and the angular segment of the bend to maintain slope and flange geometry. In this setting various sightings are taken along the pipe and the bend segments which with the use of trigonometry resolve the final flange joint plane.
This cumbersome process renders any construction assignment in which the pipe run needs to drain in a particular direction both difficult and geometrically indeterminate. For example, typical drain slopes are 1/8 or 1/4 inch per foot and any distortion or misalignment of the bend can form undrained traps or pockets that promote corrosion. Thus a continuing requirement subsists for a quick verification of the slope and its general direction as the pipe segements are welded.
Heretofore various surveying assemblies have been devised which in one or another manner provide accurate measurement of the various geometrical points and lines. Examples of such surveying assemblies are shown in U.S. Pat. No. 3,813,170 to Sears; U.S. Pat. No. 3,897,637 to Genho; U.S. Pat. Nos. 4,973,158 to Marsh; and 5,218,770 to Toga. While each describes an accurate surveying instrument, the precise and complex surveyor's procedure is not practical at each weld and therefore primarily useful to set the end references or the reference line. Alternatively, portable measuring devices have been developed incorporating complex electronic systems that render convenient most remote measuring tasks, exemplified in U.S. Pat. Nos. 5,075,977, 5,287,627 and 5,182,863, all to Rando. While suitable for the purposes intended each of the foregoing entails complex precision instrumentation that is expensive to produce and maintain and subject to damage.
A simple, inexpensive and rugged sighting assembly particularly suited to the quick slope and azimuth adjustments made in the course of welding a pipe run is desired and it is one such assembly that is disclosed herein.